Process for dynamic channel allocation in mobile radio networks

ABSTRACT

A process for dynamic channel allocation in mobile radio networks, wherein priorities which are increased or decreased in dependence on interference occurring in the channel concerned are established for the individual channels. When the propagation conditions are satisfactory, channels with low priority can be allocated. The mean of values dependent on the extent of interference can be formed in order to increase and decrease the priority. In addition, various priority lists can be established for various interference or load situations, or both.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a process for dynamic channel allocation inmobile radio networks, where priorities are established for theindividual channels and are increased or reduced as a function of theinterference occurring in the respective channel.

2. Discussion of the Prior Art

In mobile radio networks, transmissions between base stations and mobilestations go over channels that are established by at least one time sloton at least one carrier. In the case of a line-oriented transmission,one of the available channels must be allocated in establishing aconnection and in changing from one base station to another. In the caseof a package-oriented transmission, a channel must be allocated for eachcohesive segment of the link.

Various types of interference that impair the transmission quality canoccur in the channels. In addition to interference due to neighboringcells having the same frequencies, interference due to otherinterference sources can also occur, such as ignition sparks of motorvehicles, atmospheric interference and thermal noise at a low receptionfield strength. This interference is subject to fluctuations over timethat should be taken into account in the channel allocation.

A self-adaptive, learning method of dynamic channel allocation isdescribed by Y. Furuya and Y. Akaiwa, "Channel Segregation, ADistributed Adaptive Channel Allocation Scheme for Mobile CommunicationSystems," IEICE Transactions, vol. E 74, no. 6, pages 1531 ff. (June1991), and by Y. Akaiwa and H. Andoh, "Channel Segregation, ASelf-Organized Dynamic Channel Allocation Method: Application toTDMA/FDMA Microcellular Systems," IEEE Journal on Selected Areas inCommunications, vol. 11, no. 6, pages 949 ff. (August 1993). Thealgorithm used there is called "Channel Segregation" (CSEG). The knownmethod can be used with package-oriented transmission as well asline-oriented transmission. Each base station maintains a list ofpriorities for all channels available to it. After each cohesive segmentof the link, the list of priorities is incremented if there was nointerference in the transmission or is decremented if there wasinterference. Each time a new channel is allocated, the free channelwith the highest priority at the moment is always the one allocated.

Then over a period of time, a pattern of usage develops in the network,where the channels with a high priority are allocated more and morefrequently and those with a lower priority are allocated less and lessfrequently. This pattern of usage is just as static as the so-calledFixed Channel Allocation (FCA), where the available frequency resourcesare distributed uniformly over a repeating cell structure. This processthus guarantees that the channels will interfere with each other aslittle as possible with a uniform radio traffic volume. However, this isextremely inefficient when the traffic distribution is not uniform.

An improved method of dynamic channel allocation, based on the algorithmof "Channel Segregation" described above, is described by K. Hamabe, T.Ueda, T. Otsu, "Distributed Adaptive Channel Allocation Scheme withVariable C/I Threshold in Cellular Systems," 43^(rd) IEEE VehicularTechnology Conference, Meadowlands Hilton, Secaucus, N.J., USA (May1993). To achieve a more uniform channel allocation, a threshold valueis established for the carrier/interference ratio (C/I) and is set lowerfor channels with a low priority than for channels with a high priority.To do so, the available channels are subdivided into three groupsaccording to priority, where a threshold value is assigned to eachgroup.

This process ensures a more uniform utilization of the capacity of thechannels, but it does not react optimally to changes, for example, achange in traffic conditions.

SUMMARY OF THE INVENTION

A primary purpose of the present invention is to provide a process forchannel allocation in mobile radio networks that also learns from thechannel allocation in the past but permits a high utilization of theavailable channels in different traffic situations and reacts asflexibly as possible to changes.

This purpose is achieved with a process according to this invention dueto the fact that channels with a lower priority are occupied under goodpropagation conditions. With this process according to the presentinvention, channels with a lower priority are occupied more often thanwith the known process. Therefore, the efficiency of the network isimproved significantly. Furthermore, there is a greater possibility forthe initially low priority of a channel to be raised under appropriateconditions.

In this process, a threshold value, in particular thecarrier/interference ratio, that is used in testing whether a channel isto be occupied or not, is preferably a function of the priority of therespective channel. This permits an advantageous method of taking intoaccount the propagation conditions in the allocation of channels. Thefunction will preferably follow a course which starts from a constantvalue, decreases monotonically as the priority becomes lower, and ispreferably logarithmic.

The weighting of the propagation conditions and the interference can beaccomplished by various measurements, for example, of thecarrier/interference ratio, the received field strength, in mobile radionetworks with output regulation of the required manipulated variable andoptionally also the signal propagation time. Rapid adaptation of thepriorities can be accomplished in another process according to thisinvention due to the fact that to increase and decrease the priority, aquantity that depends on the extent of the interference is averaged,preferably by recursive filtering.

Another process according to this invention serves to make channelallocation dynamic due to the fact that different priorities areassigned to the channels under different interference or loadsituations, or both, where the priorities of all channels for a giveninterference situation and/or load situation are carried in a prioritylist, and when the channels are occupied, the priority to be used istaken from the priority list for the given interference situation and/orload situation. According to the prevailing situation, the priority listadapted to this situation is used for channel allocation. Therefore, thereaction time is reduced to the recognition of the respective situationor preprogrammed switching from one priority list to another.

The priority list can be selected over an entire network or inindividual regions within the network, independently of each other. Whenseveral base stations are combined into such regions, it is important tominimize the mutual influence of the boundary cells of the individualregions.

BRIEF DESCRIPTION OF THE DRAWING

The objects, advantages, and features of the invention will be morereadily perceived from the following detailed description, when read inconjunction with accompanying drawing, in which:

FIG. 1 is a flow chart illustrating the process according to thisinvention;

FIG. 2 is a schematic diagram of a first-order recursive filter; and

FIG. 3 is a chart of the input and output parameters of the recursivefilter of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The program diagrammed in FIG. 1 is started at 1 each time a channel isneeded. In the case of line-oriented connections, for example. this isnecessary when establishing the connection or in a hand-over fromanother cell. In package-oriented transmission, a free channel isoccupied with each segment of the connection.

An integer 1 representing an ordinal number of the priority list to beused in a given case, is entered into the program at 2. Integer 1 can beentered manually. However, automatic selection of the priority list canalso be performed within the scope of the invention, depending on theprevailing interference situation or load situation, or both.

In the following program part 3, the free channel with the highestpriority P is selected from the selected priority list L(1). A decisionis made at 4 whether or not the channel selected at 3 can be used. Thedecision is made as a function of whether the carrier/interference ratioCIR is larger than a threshold value CIRt, which is in turn composed ofa minimal carrier/interference ratio CIRmin and a safety margin CIRs.

In the embodiment illustrated here, the safety margin CIRs is a functionof the priority P of the channel selected. The carrier/interferenceratio CIR can be determined for the process according to this inventionduring signaling performed before the start of the connection. However,it is also possible to use values that have been determined for therespective channel by measurements in the preceding connections orsegments of connections and then stored.

The dependence of the safety margin CIRs on the priority may be givenpreferably by the function CIRs=C-f(P), where P may assume valuesbetween 0 and 1 and f(P-1)=0. Thus, channels of a high priority are usedwith a relatively low safety margin CIRS, while channels with a lowpriority must overcome a much higher safety margin. The function f(P)may be a logarithmic function, such as f(P)=log₁₀ (P).

If the carrier/interference ratio CIR is not greater than the thresholdvalue, branch 4 is followed by a program part 5 with which the nextchannel is selected from the priority list L(1). However, if it is foundthat no more channels are free, a branch 6 concerning whether theprogram was started on the basis of a new request for a connection or ahand-over is followed at 7 by a message that no connection is possibleat the present time. In the case of package-oriented connections, thedata to be transmitted are stored temporarily in an essentially knownmanner. Then the program is ended at 8.

However, if a channel with a sufficiently large carrier/interferenceratio is available at branch 4, this channel is occupied at 9. At theend of the connection or at the end of the individual segments of theconnection, it is determined at 10 whether the requirements stipulatedfor the quality of the connection or the segment of the connection aremet. This can be evaluated on the basis of the measuredcarrier/interference ratio, for example. In the event the requirementsare not met, a binary quantity i=0 is set at 11, whereas if theconnection is undisturbed, i=1 is set at 12. Using the respective valueof i, a new priority is calculated at 13, whereupon the program is endedat 8.

The selection of 1 can be made by manual input or by automaticdetermination of the interference situation and/or the load situation.Thus, for example, when there is a normal volume of communicationstraffic during the peak time of the day, a priority list L(1) can beused, whereas for special events, such as the end of an event afterwhich there is increased demand for communications, a priority list L(2)is used. To obtain a priority list adapted to the prevailing situation,program part 13 can act on this list while the corresponding situationis in existence. To do so, program part 13 can be controlled with thequantity 1 accordingly. However, it is also possible, when there arespecial situations that might not be repeated, not to save the revisedlist obtained by calculating new priorities at 13.

For example, the frequency of requests for conversations or thefrequency of the branching after "N" at 4 can be used for automaticdetermination of the respective interference situation or loadsituation, or both.

FIG. 2 shows in schematic form a recursive filter of the first order.Input signal i(n) is sent to input 21, where n is a counting variablefor designation of the successive values. At 22, i(n) is weighted with afactor A and sent over adder 23 to output 24 at which the priority P(n)is available. This is returned to adder 23 via temporary storage 25 andweighting 26 by a factor "a". In order for the priority values P(n) toremain within the range between 0 and 1, A=1-a is set. It is unnecessaryto explain additional details of a recursive filter in conjunction withthe present invention because recursive filters have been describedadequately in the literature. It is pointed out only that as "a"becomeslarger, the cut-off frequency of the low-pass filter is lower and theintegration time is longer, and the influence of previous interferencedata on the instantaneous priorities P(n) is also greater accordingly.For stability reasons, however, the value of "a"is less than 1.

FIG. 3 shows the chart for the priority P(n) as the output quantity ofthe recursive filter at the input quantity i(n) varies between thevalues 0 and 1.

In view of the above discussion it is likely that modifications andimprovements will occur to those skilled in the art, which are withinthe spirit and scope of the appended claims.

I claim:
 1. A process for dynamic channel allocation in mobile radionetworks, said process comprising the steps of:establishing prioritiesfor a plurality of individual channels; increasing or decreasing thepriorities as a function of interference occurring in each respectivechannel, where channels with a low priority are preferably occupiedrelative to channels with a high priority when there are goodpropagation conditions; and taking into account a threshold value(CIRt), in particular the carrier/interference ratio (CIR), which isused in testing whether or not a channel is to be occupied; wherein thethreshold value (CIRt) is a function of the priority (P) of therespective channel, where said function starts from a constant value andfollows a course that decreases monotonically as the priority (P)becomes lower.
 2. The process according to claim 1, wherein thedeclining course is logarithmic.
 3. A process for dynamic channelallocation in mobile radio networks, said process comprising the stepsof:establishing priorities for a plurality of individual channels;increasing or decreasing the priorities as a function of interferenceoccurring in each respective channel, where channels with a lowerpriority are preferably occupied relative to channels with a highpriority when there are good propagation conditions; and taking intoaccount a threshold value (CIRt), in particular the carrier/interferenceratio (CIR), which is used in testing whether or not a channel is to beoccupied; wherein the threshold value (CIRt) is a function of thepriority (P) of the respective channel, where said function starts froma constant value and follows a course that decreases monotonically asthe priority (P) becomes lower; and wherein a quantity that depends onan extent of the interference is averaged to increase or decrease thepriority.
 4. The process according to claim 3, wherein the averaging isperformed by recursive filtering.
 5. A process for dynamic channelallocation in mobile radio networks, said process comprising the stepsof:establishing priorities for a plurality of individual channels;increasing or decreasing the priorities as a function of interferenceoccurring in each respective channel, where channels with a low priorityare preferably occupied relative to channels with a high priority whenthere are good propagation conditions; and taking into account athreshold value (CIRt), in particular the carrier/interference ratio(CIR), which is used in testing whether or not a channel is to beoccupied; wherein the threshold value (CIRt) is a function of thepriority (P) of the respective channel, where said function is asubstantially continuous function which starts from a constant value andfollows a course that decreases monotonically as the priority (P)becomes lower.